The present invention relates generally to fluid filtration and filter assembly design, including manufacturing methods for such filter assemblies. More specifically one embodiment of the present invention relates to the design of an all-plastic, injection molded filter assembly. A snap-together assembly technique is disclosed as one option and a replaceable filter cartridge is provided as another option. In a related embodiment the shell for the filter assembly is fabricated from die-cast aluminum or steel.
Conventional metal "spin-on" water filters which are manufactured for the heavy duty market typically require a substantial number of individually manufactured components. The process technology used to manufacture these filters is mature and offers little promise of significant cost reductions. In fact, as is common with mature technology, competition in the industry is fierce. This competition has resulted in pricing pressures and a trend threatening the profitability of manufacturers.
A typical metal filter requires the following components:
1. an outer shell 6. an outer seal
2. an open endplate 7. an inner seal
3. a closed endplate 8. a centertube
4. a nutplate 9. filtration media
5. a spring 10. potting compound
Each of these components must be individually designed, manufactured, inventoried and handled in the assembly process which further drives up the overall cost. Additionally, the manufacturing processes required for some of these components include forming a rolled seam, forming threads in the nutplate and other specialized operations that add to the overall filter cost.
One recent effort to improve upon the design of the conventional metal "spin-on" filter is represented by U.S. Pat. No. 5,171,430 which issued Dec. 15, 1992 to Beach, et al. The Beach, et al. patent discloses a device which resulted from an attempt to produce a corrosion resistant (nearly all plastic), leak resistant (one piece shell with no seam), transparent filter. The Beach, et al. filter was designed to simplify the manufacturing process by reducing the number of components and the number of manufacturing steps. The Beach, et al. filter uses the following components:
1. an shell 6. an outer seal
2. an open endplate 7. an retaining ring
3. a closed endplate 8. a inner grommet
4. a centertube 9. potting compound
5. filtration media
The Beach et al. filter reduces the number of components by one compared to existing metal designs, as previously mentioned. The Beach, et al. filter eliminates the seam formation step from the manufacturing processes, a step which was also required with existing metal filter designs.
The injection blow molding process used to make the shell of the Beach, et al. filter assembly presents three concerns. One concern is the availability of several vendors to perform the somewhat specialized injection blow molding process, a process which is made even more specialized by the use of an engineering resin. The suggested plastic materials in the Beach, et al. patent are selected in part for their high resistance to the temperatures and pressures to be experienced in a diesel engine and for their resistance to the solvent action of the fluids. A further factor in the selection of the Beach, et al. materials is that they provide transparency which is ideal to enable visual inspection of the fluid condition passing through the filter.
A second concern with the Beach, et al. shell manufacturing process (injection blow molding) is that the process does not allow any inside structural contouring or shaping of the shell below the threaded region. It is well documented in plastic engineering literature that the cost advantages possible in substituting plastic for other materials are usually only realized if the design takes advantage of the multi-functionality possible with a good plastic design. Unfortunately, with no inside surface contouring available with injection blow molding, it is not possible to build in the desired multi-functionality as is enabled and disclosed by the present invention.
A third concern with the Beach, et al. injection blow molding process is that material choices are limited. The injection blow molding process is limited to amorphous materials and this limits the choices of transparent materials. This process is also limited to unfilled materials and thus excludes the use of any filled (i.e., typically 10%-30% range of filling) material. This precludes the use of lower cost opaque materials leaving the manufacturer with only relatively high priced materials as his choices, such as transparent, amorphous engineering resins.
While the Beach, et al. filter design as described in U.S. Pat. No. 5,171,430 presents certain concerns, it also has certain beneficial aspects. Since the Beach, et al. filter assembly includes a plastic shell, products marketed according to this design will soften the market to the acceptance of plastic filter assemblies. Once customers accept plastic heavy duty filters, future designs, for example those which improve upon the Beach, et al. design, will be more readily accepted. In particular, as users realize the strength and basic performance characteristics of a plastic shell design, future plastic shell designs will be easier to market.
There are other filter designs which are known to the present inventors which disclose various features and fabrication techniques which might be of interest relative to the novelty of the present invention. A representative sampling of these earlier filter designs include the following listed patents and PCT application:
______________________________________ Patent Patentee Issue Date ______________________________________ 4,036,616 Byrns July 19, 1977 5,024,761 Deibel June 18, 1991 5,118,417 Deibel June 2, 1992 ______________________________________ Application No. Applicant Publication Date ______________________________________ WO 89/01815 Thornton, et al. March 9, 1989 ______________________________________
The present invention builds upon the beneficial aspects of the Beach, et al. filter assembly and adds some redesign and various unique features to it, including a reduced number of component parts and an injection molded outer shell. The present invention also includes an injection molded, one-piece upper endplate and centertube with a snap-together assembly to the outer shell. This snap-together assembly concept involving the one-piece upper endplate and centertube may still be used when the shell is fabricated from die-cast aluminum or steel. In various embodiments of the present invention attention is given to the concept of and required structure for a replaceable filter cartridge. While the filtering element (media) of this cartridge may be securely assembled to the endplate/centertube unit, it is manually separable from that unit for disposal (incinerated) and then recycling of the plastic endplate/centertube unit.
The unique and novel features of the present invention are not found in Beach, et al. nor in any of the other listed references.